As the names respectively imply, "conjugate," "multicomponent" or "bicomponent" fibers are synthetic polymer filament materials that are formed from two or more types of polymers in adjacent relationship. The adjacent relationship can comprise a number of different arrangements and patterns as set forth in the various references cited as a part of this application. The general purpose of forming multicomponent fibers is to obtain two or more types of polymer properties in one fiber. For example, one method of bonding fibers to one another in non-woven textile fabric materials is to use a bicomponent fiber in which one component melts at a lower temperature than the other. When the correct amount of heat is applied, the lower melting component will melt and form adhering portions between the fibers to stabilize the non-woven fabric, while the other component remains solid and maintains the overall integrity of the non-woven fabric.
Other uses of bicomponent fibers are to produce fibers which will crimp naturally when heated because of the difference in the properties of the two components, for example different respective molecular orientations or different thermal properties. As known to those familiar with textiles, crimped fibers and yarns are particularly useful in clothing manufacture. Another use of multicomponent spinning technology is to produce integral filaments formed from several polymer components which can later be chemically separated to form extremely fine filaments, finer than those that would ordinarily be produced from a spinnerette head. These fine filaments are presently often referred to as "micro fibers" and demonstrate the capability to have a significant positive effect on increased consumer acceptance of polyester fabrics. This is particularly beneficial when the micro fiber fabrics exhibit desirable properties that consumers tend to favorably associate with "natural" fibers and fabrics.
One of the most common arrangements for multicomponent fibers is the bicomponent sheath-core relationship, which as its name implies, is a bicomponent filament material in which one component, referred to as the sheath, surrounds the other component which is referred to as the core.
The basic processes for forming bicomponent or multicomponent fibers are well understood. In general, separate streams of each polymer component must be directed from a supply source through a spinning head (often referred to as a "pack" ) in a desired flow pattern until they reach the exit portion of the pack; i.e., the spinnerette holes, from which they exit the spinning head in the desired multicomponent relationship. As might be expected, the design of the pack can be fairly complicated, and the manufacture of spinning heads to produce the desired flow patterns for the respective components is often similarly complex.
A recent improvement in such machinery and techniques has been set forth by William H. Hills in International Application PCT/US88/03330; International Publication No. WO 89/02938, published on Apr. 6, 1989 (the "'330 application"). The '330 application is incorporated entirely herein by reference. In this document, Hills describes a multicomponent spinning pack in which a portion of the flow paths of the respective component polymers are defined by a series of thin plates having appropriate groves or channels therein that direct the separate components to their desired positions and relationships as they exit the spinning pack in the form of a multicomponent fiber. The advantage suggested by Hills is that because the plates are relatively thin, they can be etched rather than machined into the desired flow patterns. Under some circumstances, etching is less difficult to carry out than are other processes such as casting, milling, or drilling when forming such flow paths.
The desirability of the thin etched plates also results from the potential ease with which they can be removed and replaced. Previously, the changing or cleaning of a spinning pack head for multicomponent fibers was an extremely time and labor intensive task, especially given the multiplicity of flow paths required to produce the multicomponent fibers.
The Hills apparatus is designed, however, so that many or all of the cleaning and flow path tailoring steps can be accomplished by simply removing the thin plates and replacing them with new ones. Additionally, Hills suggests that because the thin plates can be easily etched, as compared to the machining that is required for thicker plates, the production of various tailored plates, with which various tailored multicomponent fibers can be produced, will become much easier.
Nevertheless, applicants herein have attempted for some time to incorporate the teaching of the Hills publication, but without ultimate success. Specifically, it has been discovered that use of the apparatus and method as described by Hills leads to a number of problems during the spinning process, particularly when certain throughputs, polymer combinations, or sheath-core ratios are used. The most severe of these problems are the internal leakage in the spinning head combined with a "dog legging" and drip problem as the components exit the spinning head. As used in this art, "dog-legging" refers to the tendency of a stream of molten polymer to bend as it exits a spinnerette, rather than flowing in a straight path. If the bend in the dog leg is severe enough, the polymer stream will literally return and contact the spinnerette, and then drip inappropriately from it.
As best understood by the applicants, it appears that in the Hills apparatus the components tend to mix within the spinning head prior to the point, or just adjacent the point, at which they exit the spinning head. This is referred to as an "internal leak." The result is a fiber mixture that has been brought together prematurely and in which the desired sheath-core or other pattern relationship has been lost. The resulting fiber is either undesirable, or even useless, for its intended purposes.
Additionally, under certain circumstances the polymer will visibly leak from the pack at undesired and unintended positions, a problem referred to as an "external leak." At present, it appears and is assumed that external leaks are also indicative of internal leaks as just described.
In spite of these difficulties, the potential for the Hills type of apparatus appears to be quite good and it would be useful if methods and techniques could be developed that would permit the use of the thin plates in a spinning pack while eliminating the problems experienced in such devices to date.
It is thus an object of the present invention to provide a method of using a Hills type apparatus successfully in the production of bicomponent fibers and while eliminating the problems that to date have been inherent in any such use of Hills type machinery.
The foregoing and other objects, advantages and features of the invention, and the manner in which the same are accomplished, will become more readily apparent upon consideration of the following detailed description of the invention taken in conjunction with the accompanying drawings, which illustrate preferred and exemplary embodiments, in which: